The capture of the 850-year-old mosque was considered a big symbolic victory to Iraqis. It is where ISIS leader Abu Bakr al-Baghdadi announced its caliphate almost three years ago.

“The return of Nuri mosque and minaret of Hadba today after being [destroyed] by ISIS marks the end of Daesh State falsehood,” said al-Abadi, adding “we will continue chasing ISIS until we kill and arrest [every] last one of them.”

Women and children flee fighting in Mosul's Old City on Friday. STR / EPA

Fighting remained intense, however. Commanders of counter-terrorism units fighting their way through the warren of narrow streets say die-hard ISIS fighters are dug in among civilians and the battle ahead remains challenging, according to Reuters.

Work told NBC News it is hard to know how many ISIS fighters were left inside the Old City.

“I’m not sure it really matters because the Daesh fighters that are in there are going to fight to the death,” he said, referring to ISIS by an Arabic acronym.

Tens of thousands of civilians remain trapped in the city with dwindling supplies of food, water and medicine, according to Reuters.